Early Growth and Protein-Energy Metabolism in Chicken Lines Divergently Selected on Ultimate pH

Abstract

In chickens, a divergent selection on the Pectoralis major pHu allowed the creation of the pHu+ and pHu- lines, which represent a unique model for studying the biological control of carbohydrate storage in muscle. The present study aimed to describe the early mechanisms involved in the establishment of pHu+ and pHu- phenotypes. At hatching, pHu+ chicks were slightly heavier but exhibited lower plasma glucose and triglyceride and higher uric acid. After 5 days, pHu+ chicks exhibited higher breast meat yield compared to pHu- while their body weight was no different. At both ages, in vivo muscle glycogen content was lower in pHu+ than in pHu- muscles. The lower ability of pHu+ chicks to store carbohydrate in their muscle was associated with the increased expression of SLC2A1 and SLC2A3 genes coding glucose transporters 1 and 3, and of CS and LDHα coding key enzymes of oxidative and glycolytic pathways, respectively. Reduced muscle glycogen content at hatching of the pHu+ was concomitant with higher activation by phosphorylation of S6 kinase 1/ribosomal protein S6 pathway, known to activate protein synthesis in chicken muscle. In conclusion, differences observed in muscle at slaughter age in the pHu+ and pHu- lines are already present at hatching. They are associated with several changes related to both carbohydrate and protein metabolism, which are likely to affect their ability to use eggs or exogenous nutrients for muscle growth or energy storage.

Keywords: carbohydrate metabolism; chicks; glycogen; metabolism; muscle; protein synthesis.

Figure 1

Plasma concentration in glucose (glycemia, A), uric acid (B), and triglyceride (C) measured at hatching (D0) and 5 days post-hatching (D5) in the pHu+ and pHu− lines. Data are presented as mean ± SEM; n = 15 per line and per age. Different letters indicate significant differences between muscle groups (p ≤ 0.05).

Figure 2

Periodic acid-Schiff staining of Pectoralis major muscle cross-sections from pHu+ (A,C) vs. pHu− (B,D) at hatching (D0, A,B) and 5 days post-hatching (D5, C,D). Scale bar = 13 μm (A,B) and 25 μm (C,D).

Figure 3

Ultimate pH in Pectoralis major muscles at hatching (D0) and at 5 days post-hatching (D5) in the pHu+ and pHu− lines. Data are presented as mean ± SEM; n = 6 per line and per age at D0 and D5.

Figure 4

Immunolocalization (A–D) and quantification (E) of sarcomeric myosin (MF20) on satellite cells derived from Pectoralis major muscles sampled at hatching (D0) and 5 days post-hatching (D5) in the pHu+ and pHu− lines. Scale bar = 70 μm. Data are expressed as mean ± SEM. Different letters indicate significant differences between muscle groups (p ≤ 0.05). The anti-vinculin antibody was used as a loading control.

Figure 5

Regulation of the S6K1 pathway in the Pectoralis major muscles sampled in the pHu+ and pHu− at hatch (D0; A) and in the cell culture of satellite cells from Pectoralis major muscles sampled at hatching (D0) following insulin stimulation (100 nM for 0, 15, or 45 min; B). Membranes were incubated with polyclonal antibodies against phospho-S6K1 [T389] (pS6K1 T389), S6K1, phospho-S6 [S235/236] (pS6 S235/236), and ribosomal protein S6. Vinculin was used as loading control. Data are expressed as mean ± SEM.